PRINCIPLE OF THE JFET

In a JFET, the current varies because of the effects of an electrical field within the device. Electrons or holes move along a current path called a channel from the source (S) electrode to the drain (D) electrode. This results in a drain current I_D that is normally the same as the source current I_S. The drain current depends on the voltage at the gate (G) electrode. As the gate voltage E_G changes, the effective width of the channel varies. Thus fluctuations in E_G cause changes in the current through the channel. Small fluctuations in E_G can cause large variations in the flow of charge carriers through the JFET. This effect makes it possible for the device to act as a voltage amplifier.